The present invention relates generally to cardiac pacemakers. More particularly, the present invention relates to cardiac pacemakers for treating atrial fibrillation.
An arrhythmia is a heart rhythm disorder which interferes with the life sustaining blood circulation activities of the heart. Examples of arrhythmias include ventricular fibrillation and atrial fibrillation. Ventricular fibrillation affects the lower chambers of the heart (the ventricles) and atrial fibrillation affects the upper chambers of the heart (the atria). Ventricular fibrillation is a rapid and disorganized firing of muscle fibers within the ventricular myocardium. During ventricular fibrillation, the ventricles do not contract in an organized manner, no blood is pumped, and blood pressure falls to zero. Patient death may occur within 4 minutes from the onset of ventricular fibrillation. Companies such as Medtronic, Inc., have developed implantable defibrillators which may be used to successfully treat ventricular fibrillation by delivering a defibrillating shock to the heart when fibrillation is detected.
Atrial fibrillation occurs more frequently than ventricular fibrillation. It has been estimated that atrial fibrillation affects more than million people worldwide. As people age, their chances of developing atrial fibrillation increase dramatically. In fact, approximately 70% of all people with atrial fibrillation are over 65 years of age. Although atrial fibrillation occurs with great frequency, successful therapies for atrial fibrillation have been difficult to identify.
The symptoms of atrial fibrillation may include shortness of breath, loss of the ability to exercise, chest pain, rapid heart beating, light headedness, and loss of consciousness. When atrial fibrillation occurs, the upper chambers of the heart (the atria) rapidly quiver instead of contracting in an organized manner. The atria of the heart may beat/quiver at a rate of between 350 and 600 times per minute during an episode of atrial fibrillation.
Because the pumping function of the upper chambers does not work properly during atrial fibrillation, blood is not completely emptied from the heart""s chambers, causing it to stagnate in the upper chambers of the heart. Over time, clots may form in this stagnant blood. Occasionally, clots may break free and enter the blood stream. When one of these blood clots lodges in the blood vessels of the brain, a stroke may result. It has been estimated that atrial fibrillation is responsible for over 70,000 strokes each year. Because treating atrial fibrillation is an important way to prevent strokes from occurring, the American Heart Association has called for aggressive treatment of atrial fibrillation.
The present invention relates generally to cardiac pacemakers. More particularly, the present invention relates to cardiac pacemakers for treating atrial fibrillation. The structures and methods in accordance with the present invention may be utilized to reduce the likelihood of atrial fibrillation in a heart. One such method comprises the steps of selecting a desired ventricular rate and pacing the ventricle of the heart at this desired ventricular rate.
In certain implementations, the atrium of the heart is paced at twice the desired ventricular rate while the desired ventricular rate is less than a preferred rate. In these advantageous implementations, the atrium of the heart is paced at the desired ventricular rate while the desired ventricular rate is greater than the preferred rate. The preferred rate may be selected to match a particular patient, for example, by taking into account physical characteristics of that patient.
In other implementations, the atrium of the heart is paced at an advantageous atrial rate while the desired ventricular rate is greater than the preferred rate. While the desired ventricular rate is less than the preferred rate, the atrium of the heart may be paced at twice the desired ventricular rate.
In one aspect of the present invention, an atrial pulse is delivered synchronously with each ventricle pulse. In another aspect of the present invention, a ventricular pulse is delivered substantially synchronous with each atrial pulse while the desired ventricular rate is greater than the preferred rate. While the desired ventricular rate is less than the preferred rate, a ventricle pulse may be advantageously delivered synchronously with one out of two atrial pulses. The synchronous arrangement allows an offset between atrial and ventricular pulses.
In certain implementations, the step of selecting the desired ventricular rate may include the steps of sensing spontaneous ventricular signals, and determining a desired ventricular rate in response to the sensed ventricle signals. Methods in accordance with the present invention may include the step of severing a conductive path between the atrium and the ventricle as one of many preferred surgical procedures in implementing one aspect of the present invention. The step of severing the conductive path between the atrium and the ventricle may comprise, for example, the step of ablating an A-V node of the heart.
A pacing system in accordance with the present invention may include a pacemaker having a controller. The controller may comprise, for example, a microprocessor. The controller may direct a ventricular pulse generator of the pacemaker to provide pacing pulses to a ventricle via one or more leads coupled to one or more ventricular electrodes. The controller may also direct an atrial pulse generator to provide pacing pulses to an atrium via one or more leads coupled to one or more atrial electrodes. The atrial pulse generator and the ventricular pulse generator may each include one or more capacitors, and a switching circuit capable of charging the capacitor(s) by coupling the capacitor(s) to an energy source and discharging the capacitor(s) through the electrodes.
A pacemaker in accordance with the present invention may also include a signal processor for sensing and processing spontaneous signals from heart. Spontaneous signals from the heart may be used in determining a desired ventricular rate. In some implementations of the present invention, the signal processor may include one or more amplifiers, and one or more filters. Further rate responses may be established using methods and structures disclosed in U.S. Pat. No. 5,052,388 to Sivula which is incorporated herein in its entirety by reference.
A pacemaker in accordance with the present invention may further include a memory. The memory may be used to store operating instructions for the controller. The memory may also be used to store values in accordance with the present invention. Examples of values that may be stored include a preferred rate and a desired ventricular rate and/or a desired atrial rate. The pacemaker may also include a telemetry antenna. The telemetry antenna may be used in conjunction with the controller to load instructions and values into the memory.